1. Field of the Invention
The present invention relates to a method for lubricating a compression type refrigerating system. More particularly, it relates to a method for lubricating a compression type refrigerating system efficiently without detracting wear resistance, cooling effect and stability by employing a mixed refrigerant comprising 1,1,1,2-tetrafluoroethane (R-134a) and 1,1-dichloro-2,2,2-trifluoroethane (R-123) as the essential component or a mixed refrigerant comprising 1,1,1,2-tetrafluoroethane (R-134a) and chlorodifluoromethane (R-22) as the essential component in combination with either or both of a specific hydrocarbon compound and polyglycol as the lubricant.
2. Description of the Related Arts
Conventionally, in a compression type refrigerating system or cycle comprising a compressor, a condenser, an expansion valve or a capillary tube and an evaporator, a fluorinated hydrocarbon compound such as dichlorodifluoromethane (R-12) has been used as the refrigerant. Many lubricants compatible with the refrigerant have also been made industrially available for use.
However, there have been misgivings that these fluorinated hydrocarbon compounds (hereinafter referred sometimes to as "flon compound") conventionally used as the refrigerant are liable to cause depletion of the ozone layer after they are released into the open air. Throughout the world, so-called substitute flon refrigerants have come into the use, replacing these fluorinated hydrocarbon compounds. The replacement has been realized by the development and marketing of refrigerants comprising substitute flon compounds such as 1,1,1,2-tetrafluoroethane (R-134a), 1,1,2,2-tetrafluoroethane (R-134b), 1,1-dichloro-2,2,2-trifluoroethane (R-123), 1-chloro-1,1-difluoroethane (R-142b) and 1,1-dichloro-1-fluoroethane (R-141b).
Of these substitute flon refrigerants (flon refrigerants), the present trend has been such that the use of R-134a is encouraged to replace conventional R-12 or R-22.
Generally, the substitute flon refrigerants are different from conventional flon refrigerants in characteristics in that they have poor miscibility with mineral oils which have been used chiefly in combination with the conventional flon refrigerants. Thus, synthetic oils such as polyalkylene glycol compound (PAG) or ester compound have been developed and come into use as the suitable lubricant for these substitute flon refrigerants (U.S. Pat. No. 4,755,316 and Japanese Patent Application Laid-Open No. 33193/1991).
However, even for these synthetic oils, certain problems have awaited the solution with respect to the substitute flon refrigerants. PAGs or esters have a good miscibility with R-134a, a substitute flon refrigerant but not a sufficiently high stability.
Some hydrocarbon compounds such as mineral oil have a high stability to R-134a but are not miscible well with this substitute flon. A lubricant capable of satisfying the requirement both of miscibility and stability has been found hard to obtain.
Furthermore, R-134a has a high vapor pressure and thus can be used singly in compression type refrigerating systems. But R-123 having a low vapor pressure cannot be used singly elsewhere but for turbo type refrigerators and further something is missing in R-123 with respect to wear resistance, cooling effect and the like.
The present inventor has made intensive studies with methods for lubricating compression type refrigerating systems by using R-134a which is better than other substitute flon refrigerants.
As the result, it has been found that the compression type refrigerating systems can be efficiently lubricated by means of the simultaneous use of R-134a and another substitute flon refrigerant or a conventional flon refrigerant in combination with a specific lubricant.